Matlab missing dependency MEX-file - matlab

Question

I have a script in matlab that calls other libraries. I use matlab version 2012a on linux . I get below error and I don't know how to fix it.
The error is :
Invalid MEX-file '/home/XXX/nearest_neighbors.mexa64':
libflann.so.1.8: cannot open shared object file: No such file or
directory
Error in flann_search (line 82)
[indices,dists] = nearest_neighbors('find_nn', data, testset, n, params);
Error in MyScript (line 73)
[nresult, ndists] = flann_search(Ntraindata', Ntraindata', resu.KNN, struct('algorithm','composite',...

Answer 1

That library you are referring to - https://github.com/mariusmuja/flann/ - has the nearest_neighbors function written in MEX code. MEX code is C code that is used to interface with MATLAB. People usually write heavily computationally burdening code over in MEX as it is known to handle loops and other things faster. The inputs come from MATLAB and are sent to this MEX function, and the outputs come from the MEX function and are piped back to MATLAB. It's basically a nice black box where you can use it just like any other MATLAB function. In fact, a lot of the functions that come shipped with MATLAB have MEX wrappers written to promote acceleration.
You are getting that error because you need to compile the nearest_neighbors function so that there is a MEX wrapper that can be called in MATLAB. That wrapper is missing because you haven't compiled the code.
First, you need to set up MEX. Make sure you have a compiler that is compatible with your version of MATLAB. You can do that by visiting this link:
http://www.mathworks.com/support/compilers/R20xxy/index.html
xx is the version number that belongs to your MATLAB and y is the character code that comes after it. For example, if you are using R2013a, you would visit:
http://www.mathworks.com/support/compilers/R2013a/index.html
Once you're there, go to your Operating System and ensure you have one of those supported compilers installed. Once you have that installed, go into MATLAB, and in the command prompt, type in:
mex -setup
This will allow you to set up MEX and choose the compiler you want. Given your error, you're using Linux 64-bit, so it should be very easy for you to get GCC. Just make sure that you choose a version of GCC that is compatible with your version of MATLAB. Once you choose the compiler, you can compile the code by doing this in the command prompt:
>> mex -v -O nearest_neighbors.cpp
This should generate the nearest_neighbors MEX file for you. Once that's done, you can now run the code.
For more detailed instructions, check out FLANN's user manual - http://people.cs.ubc.ca/~mariusm/uploads/FLANN/flann_manual-1.8.4.pdf - It tells you how to build and compile it for MATLAB use.
Good luck!